Question

Lab 12: Saponification – Making Soap

Objective:

To make soap using the process call saponification, an organic form of the neutralization reaction that an acid reacts with a base to form a salt.

Introduction:

A soap is the sodium or potassium salt of a long chained carbohydrate called a fatty acid.  A fatty acid usually contains between 12 – 18 carbon atoms. Fatty acids are esters of either animal or vegetable fats.  They are called triglycerides if they are solids at room temperature and oils if they liquid at room temperature.  

The fats and oils that are most common in the preparation of soaps are lard and tallow from animal sources and coconut, palm and olive oils from vegetable sources.  

Saponification reaction:

                           

                            O

                           ║

CH₂ — O — C — (CH₂)₁₄CH₃                                                                       CH₂  — OH                                                                                                                                                                           

                            O                                                       

                         ║

CH —  O — C — (CH₂)₁₄CH  +   3 NaOH                                                CH —  OH    +    3 CH₃(CH₂)₁₄COO^-Na⁺

                                                                                                                                                                                  

                     O                                                                                                          SOAP

                      ║

CH₂—  O — C — (CH₂)₁₄CH₃                                                             CH₂  — OH     

                                                                      GLYCEROL

Materials needed:

         Vegetable oil (either pure (100%) corn, canola or sunflower)

         A source of NaOH (Drano® from Titration experiment)

         25 mL graduate cylinder

         100 mL beaker

         25 mL Erlenmeyer flask

         Weighing boats

         

Procedure:

Note: wear gloves (and goggles of course) as sodium hydroxide is caustic. Note: Please do not use the soap that you make, but, dispose of the soap when the lab is completed.

1. Dissolve 3.25 g of sodium hydroxide in 8 mL of water in a 25 mL

Erlenmeyer flask.   Swirl to help dissolve the solution. Set aside and allow to cool to between 35°C and 40°C or 95°F – 100^oF

2. In a beaker add 25 grams of your pure oil and heat gently (use a hot water

bath) to between 35°C and 40°C or 95°F – 100^oF.

3. Combine the sodium hydroxide solution and oils. Stir the mixture until it

starts to harden (about 15-20 minutes).  Once the mixture starts to harden then stir for 5 minutes at 15 minute intervals. Make sure the temperature of the hot bath stay above 35°C or 95°F.   At the point when it starts to harden you can also add any ‘essential oil’ ingredients to scent your soap.  

4. Once the soap is relatively firm (your stir marks will remain for several

seconds) pour raw soap into your prepared molds or keep it in the beaker. After a few days the soap can be turned out of the mold. If the soap is very soft, allow it to cure for a few days to firm the outside.

5. Eventually remove the soap and set the bar out to cure and dry. This will

allow the bar to firm and finish saponification. This can actually take days

to cure properly. The longer you wait the less unreacted sodium hydroxide

will be present

Saponification – Making soap

REPORT FORM:         Name ________________________

                                    Date _________________________

What are the fatty acids in corn oil.

What are the fatty acids in canola oil.

What was the texture and color of your soap.

Write the structure for the soap you made.  Remember the oil you used.